IE45978B1

IE45978B1 - Method for the preparation of perlite structures

Info

Publication number: IE45978B1
Application number: IE2245/77A
Authority: IE
Original assignee: Dicalite Europe Nord
Priority date: 1976-11-09
Filing date: 1977-11-03
Publication date: 1983-01-12
Also published as: NO773813L; AU3051377A; JPS5846468B2; JPS5360884A; IT1087430B; DE2749100C3; GB1556832A; AU508821B2; NO144700B; DE2749100A1; NL7712324A; ES463970A1; CA1107911A; FR2370008A1; FR2370008B1; US4179264A; BR7707463A; IE45978L; NO144700C; DE2749100B2

Abstract

Particulate unexpanded perlite is introduced to an expansion apparatus that utilizes the combustion of a gas as a source of heat. The particulate perlite is mixed with a combustible gas, air from a first source and oxygen and thereafter introduced to a burner section. The amount of oxygen introduced is in the range of from 1.5 to 16 weight percent of the amount of air introduced. The amount of combustible gas in the mixture is related to the air input from the first source, being in the range of 1 volume of combustible gas to 2 to 6 volumes of air.

Description

The present invention relates to a method of making expanded perlite structures having advantageous properties for numerous uses, particularly as filtering aids.

Perlite is a silicious material of volcanic origin, which has by weight 5 a silica content greater than 65% and a catibined water content of 2 to 5%.

In addition to silica and water, perlite contains variable quantities of compounds of aluminium, sodium and potassium among others.

When perlite ore in the form of particles is introduced into a flame, it is subjected to expansion or bursting into a material of lighter weight and density. Generally speaking, the expansion or bursting is observed when the perlite is heated to a temperature of 760 o to 1315 C, depending upon the origin of the perlite and its particle size.

Ordinarily temperatures of 870 to 1150°C are used.

As a general rule, it can be said that a perlite ore has a density of □ 0.96 to 1.28 kg/dm , whereas, after expansion, the density is 0.032 to 0.16 kg/dm\ Various techniques for the expansion of perlite are already known and have met with varying degrees of success. By reason of the continuing rise in demand for expanded perlite of better quality and at a lower cost, it 2o is desirable to provide a production method enabling a substantial increase in the capacity of known expansion installations, without a substantial investment of capital.

It is the object of the present invention to provide such a production method.

According ίο the preser.f invention fnere is provided σ method of preparation of expana'ed perlite structures, comprising the introduction of non-expanded particles of perlite into an expansion apparatus, end the heat treatment of these non-expanded particles by means of a burner for a period of time sufficient to produce the expansion of substantially al! the expansible particles of perlite, wherein there if used at the burner of the expansion apparatus a mixture of combustible gas, air, and oxygen, In the relative quantities assuming the same temperatures and pressures of I volume of combustible gas to 2 to C volumes of air, and 1.5 to 15% by weiaht of oxygen relative to the air used.

Preparatory to carrying out the method according to the invention, the perlite used is ground, generally speaking, tc a particle sice of less than 2.5 cm, ond is dried to a moisture content of less than 0.2% by weighi, by treatment at 26-94°C for 10 minutes, which constitutes the method frequently used in practice.

The material is then ground more finely and subjected to sorting or classification to provide the starting material for the method according to the invention.

The starting material used in the method according to the invention should preferably all pass through a screen with o mesh opening of 595 microns. It is preferable that the greater part of the material be retained on a screen with a mesh opening of 1OO microns, a large part being retained on a screen with openings of 297 microns and a large parr of the remainder being retained on o screen with openings of 150 microns, it is advantageous, in order to achieve maxima! results, that appreciable quantities of the material be of o size smaller than 74 microns, for example 2 to 20%. A typical by v.eight analysis of the particle sizes -3^5978 (A.S.T.M. E Ii—6!) of a storting material which can be used is os foDows:595 microns and less 297 - 595 microns 150 - 297 microns 100 - 150 microns - IOO microns less than 74 microns 100% to 60% to 60% to 20% to 20% to 20% A particularly advantageous starting material will have the following approximate percentages by weight of screen retention: 297 - 595 microns 150 - 297 microns IOO - 150 microns 74-100 microns less than 74 microns to 30% to 50% to 20% to 12% to 15% The unexpanded perlite may be fed to the expansion apparatus by traditional methods, and introduced therein at such a rate that practically all of this perlite will undergo an expansion under the conditions which will be explained more completely below. According to the ordinary methods of expansion of perlite, air is mixed with a combustible gas, such as natural gas, and the mixture is fed to 20 the burner of the expansion apparatus. The flows and the quantities of air and natural gas (principally methane) vary according to the ordinary requirements of the known methods, and according to the characteristics of the burner and the expansion apparatus. As a matter of fact, satisfactory use can also be made in the process according to the invention of other combustible gases, e.g. propane or butane. -445S78 ll is frequently desirable, ia order ' direct and control the process, and io he able to enjoy the advantages of a heat exchange, to augment the initial air feed by an additional cr secondary air feed. If this technique is used, the secondary air is ordinarily fed at a point in the expansion apparatus different from the feed point of the primary air. In the traditional expansion apparatus of the vertical type, a secondary air feed is ordinarily introduced at a point lying weil above the position of the burner.

In the process according to the invention, a natural gas is mixed with primary air and oxygen, and this mixture is fed to the burner. One critical characteristic of the method of the present invention is the quantity of oxygen which is added relative to the primary air feed. On the basis of percentages by weight, it is necessary to feed oxygen io the combustible gas mixture going to the burner at the rate of 1.5 to 16¾ relative to the air present in this gas mixture. It is more particularly preferable to use from 2.5 -to 10’ oxygen relative to the quantity of air in the initial gas mixture.

Another characteristic which is vital to the success of the process according to the invention, is the ratio by’ volume of ccrrbustible gas to primary air fed to the burner. Thi.s ratio, when given in volumes assuming the sane tenperature and pressure is 1:2-6 (ccrrbustible gas/primary.air) and preferably 1:2—1.

The secondary air is fed tc ensure complete combustion of the natural gas mentioned above. This secondary air ran be introduced in any convenient way, and at a traditional point. Nevertheless, a typical example of embodiment according to the method -of the invention provides for the use of a vertical expansion apparatus in which the secondary air is introduced into a double or triple-enclosure structure in order to participate ir. the heat-exchange -S” advantages, and to ensure the introduction into the burner zone, ciose to the base of the latter in particular.

Preferred results from the method of the invention are obtained by using 2 to 4 volumes of air to I volume of combustible gas with an introduction of oxygen in quantities varying from 1.5 to 16% by weight relative to the quantify of primary air used.

According to a particular form of embodiment, in which a vertical expansion apparatus is used, there is employed a mixture of: 235 m / hour of natural gas 3 Iq 540 m /hour of normal primary air, and to 60 m / hour of Oxygen.

Secondary air is introduced in a quantity of 1680m /hour at the base of the burner.

A high yield of a product constituting o filtering aid is obtained, with improved air permeability and lower weight. The product also exhibits a lower filter cake density and yields a minimum quantity of floating material and waste. The said particular form of embodiment was repeated in identical fashion, except that oxygen was not added to the mixture of natural gas and normal primary air. A quantity of product was obtained amounting to only 75% of the quantity 2o obtained with the use of the particular form of embodiment of the present invention described above.

Typical yields obtained with the use of the method of the invention are as follows, compared with yields obtained with traditional techniques: -64 59 7 8 Product Traditions] Method of technique the invention.

Flow at medium speed . 0 9 FT 96% Flow at medium speed. 90% 95%, 5 Flow at high speed. 76% 85%, Flow si high speed. 70%. 90% In addition to the above improvements in yield, reject material is reduced by at least 50% due to the use of tne process of tne invention. The products described in the preceding table relate, of course, to the desired primary 3.0 product. We also obtain ecrresoadwg small quantities of low yield filtration aid collected according to known methods. in addition to the advantages of the invention disclosed above, it will be evident to the specialist that the method of the invention, by increasing capacity, will at the same time reduce depreciation and, owing to the increasing P5 cost of natural gas, also make possible a reduced total cost of use.

S3 ?g

Claims

CLAIMS:

I. A method of preparation of expanded periite structures, comprising the introduction of non-expanded particles of perlite into an expansion apparatus, and the heat treatment of these non-expanded particles by means of a burner for a 5 period of time sufficient to produce the expansion of substantially all the expansible particles of perlite, wherein there is used at the burner of the expansion apparatus a mixture of combustible gas, air, and oxygen, in the relative quantifies assuming the same temperature and pressure of I volume of combustible gas to
2. To 6 volumes of air, and 1.5 to 16% by weight of oxygen relative to the air used. 10 2. A method according to claim I, wherein there is used I volume of combustible gas to 2 to 4 volumes of air.
3. A method according to claim I or 2, wherein oxygen is used at the rate of 2.5 to IO% by weight relative to the air employed.
4. A method according to claim I, 2 or 3 wherein the non-expanded 15 perlite particles constituting the starting material have a particle size of less than 595 microns with a size distribution as follows: 297 - 595 microns 20 to 00% 150 - 297 30 to 60 % 100-250 2 to 20 % 74-100 2 to 20% less than 74 microns 2 to 20% 5. A method according to claim 4, wherein the non-expanded perlite forming the starting material has a particle size of less than 595 microns -84 5 9 7s and a size distribution es rois 297 - 595 microns 150 - 297 IOO - i50 20 to 30% 30 to 50/
5. To 20 7 5 74 - iOO ” 5 to 12 / less than 74 microns 5 to 15 /
6. A method according to arty preceding claim wherein the combustible gas is a natural gas.
7. A method according to any preceding claim wherein a secondary 10 feed of air is used in at least the quantity necessary to ensure complete combustion of the combustible gas.
8. A method of producing expanded perliie structures substantially as hereinbefore described.
9. Expanded perlite structures produced by a method according to 15 any one of the preceding claims. MACLACHLAN & DONALDSON, Applicants' Agents, 47 Merrion Square,